This thread came up when I Googled "blackberry jar loader" but it doesn't tell you a really quick way of doing this on an 8830. I found this on pinstack and thought it worth sharing:

Hook up your USB cable and copy the jar & jad files using Explorer. I put it on my uSD card but I assume you can use device memory too. Then open the Media app and push the BB button to get to Explore. Find the .jad file and click on it. Installation behaves just like OTA from here on out.